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Re: writing to parameter / type-switch
- From: Per Bothner <per at bothner dot com>
- To: kawa at sourceware dot org
- Date: Sat, 29 Nov 2014 10:07:26 -0800
- Subject: Re: writing to parameter / type-switch
- Authentication-results: sourceware.org; auth=none
- References: <5479E1AF dot 4030207 at hungry dot com>
On 11/29/2014 07:09 AM, Seth Alves wrote:
I'm trying to run some code that does roughly this:
(define (foo . opt)
(set! opt (if (null? opt) #f (car opt)))
opt)
(display (foo 1))
(newline)
./kawa-type-switch.scm:7:13: warning - type java.lang.Boolean is incompatible with required type list
./kawa-type-switch.scm:7:3: warning - cannot convert literal (of type java.lang.Boolean) to Type list
Value '1' for variable 'opt' has wrong type (integer) (gnu.math.IntNum cannot be cast to gnu.lists.LList)
at kawa$Mntype$Mnswitch.foo$V(kawa-type-switch.scm:7)
at kawa$Mntype$Mnswitch.applyN(kawa-type-switch.scm:6)
...
I can work around it, but is there a way to make kawa happy with this?
The reason is that Kawa automatically sets the type of a dotted parameter to 'list'.
Conceptually the fix is to implicit treat:
(define (foo . opt) ...)
as:
(define (foo . incoming-opt::list)
(let ((opt incoming-opt)) ...))
We're not going to make this change until I make make sure no
extra code is generated in the normal case where the parameter isn't assigned to.
That isn't in principle difficult, but it means either awkwardly adding a
Scheme dependency in the non-Scheme-specific code - or Kawa needs to be
smart enough to combine variables when variable2 is initialized to variable1
and neither is further modified.
Shortly I will be working on changing how parameter are processed, partly to
support ML-style pattern matching. It's not a priority right now.
If you want to enter a bug in the Kawa BugZilla that will make it easier
to not forget it ...
I'm not considering this a high-priority bug because of the easy work-around and
because frankly I consider the example pretty horrible style ...
--
--Per Bothner
per@bothner.com http://per.bothner.com/